1. Field of the Invention
The invention concerns a coating product sprayer device with a rotary sprayer member, for example a sprayer bowl rotating at high speed as commonly used in the automobile industry in particular; it is more particularly concerned with an improvement enabling quick and effective cleaning of all parts of the rotating member using a relatively small amount of cleaning product.
2. Description of the Prior Art
In the electrostatic painting art use is often made of rotating members for spraying the coating product, especially bowl-shape members. A rotating member of this kind is rotated at high speed (usually between 20,000 and 30,000 revolutions per minute) by a turbine and is held at a high voltage. The shape of the bowl is somewhat complex, which raises problems with cleaning. In the automobile industry cleaning in order to change the coating product must be quick. Cleaning is usually done by spraying a cleaning product (solvent) onto the various parts of the sprayer member while it is rotating at high speed. This raises various problems.
One is to clean the front part of the sprayer member, which requires the use of a mobile cleaning product sprayer nozzle to reach the front part, as it is not possible for the nozzle to remain in the jet of sprayed coating product between cleaning operations. It is therefore necessary to provide an actuator and an associated control system so that the nozzle can be retracted and a Venturi suction device to collect any droplets of the cleaning product which might escape during spraying. The operation of a mechanism of this kind is never entirely satisfactory because in a coating product sprayer installation the mechanisms which are moved only from time to time are characterized by poor reliability, because of stray sprayed material soiling the interfaces.
Another problem is that of splashing when the cleaning product is sprayed onto the bowl rotating at high speed. To prevent such splashes reaching adjacent parts, and in particular the objects to be coated, French patent No. 1 245 081 proposes to carry out the cleaning inside an interceptor, a kind of mobile casing, which is moved axially by actuators to surround the sprayer member completely while it is sprayed with multiple jets of cleaning product from nozzles of which some move with the interceptor. The interceptor is provided with suction means for recovering and evacuating the cleaning product, entraining coating product residues. The equipment is bulky and costly. It is not reliable in operation for the reasons already explained.
The document DE-U-8607841 describes a rotating bowl sprayer device in which the frustoconical exterior surface of the bowl can be cleaned by divergent jets of solvent from nozzles in the support enclosing the drive means for the rotating bowl. The characteristics of liquids are such that this divergence can be achieved only by a jet sprayed in the form of droplets. The droplets are entrained by the air which is caused to rotate by the bowl, reducing efficiency. According to the teaching of this document, the sprayed solvent which impinges on the surface to be cleaned over substantially all of its axial length is then ejected radially by centrifugal force, which causes significant splashing.
The invention makes it possible to solve all these problems and proposes an arrangement without any mobile cleaning nozzle and/or interceptor. The equipment is therefore less costly and its operation is more reliable. A smaller quantity of cleaning product is used.
The invention is based on the surprising finding that splashing of the cleaning product due essentially to cleaning generally convex parts of the sprayer member can be eliminated (despite the centrifugal acceleration of several tens of thousands of m/s.sup.2 which tends to eject the coating product radially) by exploiting other phenomena tending to hold the film of coating product onto the surface such as, feasibly, surface tension and the Coanda effect.